1. Field of the Invention
The present invention relates generally to antennas, and more particularly a class of low cost impulse compatible wideband antennas.
2. Discussion of Background Art
Radio frequency (RF) energy, also known as electromagnetic radiation (EMR), is an electromagnetic wave that propagates through circuits and under the right circumstances, through free space. Antennas are a critical part of many products and systems for transmitting and receiving free-space RF. Antennas are used to efficiently convert energy from a circuit or transmission line (wires) to free space.
Wide bandwidth antennas are a special sub-class of antennas that can transmit over a wide range of frequencies. Presently, new technologies are being developed using Micro-Impulse Radar (MIR). MIR based devices are useful for inspecting highways and bridges, underground object detection, and behind walls. MIR can also be useful for communications, and other microwave sensor operations, such as that described in U.S. Pat. No. 5,361,070, entitled xe2x80x9cUltra Wideband Radar Motion Sensor,xe2x80x9d issued on Nov. 1, 1994 by inventor Thomas E. McEwan.
Standard wideband antennas have a horn design and require machined tolerances, which are difficult to make and often have a low yield. As a result, over thirty percent of the cost of a typical radar systems is for its antenna and catalog broadband antennas typically cost into the several thousands of dollars.
MIR signals however, not only contain frequencies across a broad range, but often have a large low frequency (and even DC) components that easily reflect back into the microwave system causing ringing and feedback noise. Many standard antennas are particularly susceptible to reflections due to impedance mismatching. Pulse dispersion (the tendency to radiate different frequencies from different portions of the antenna) is also a problem with standard wideband antennas. Thus, antennas which transmit MIR signals, also known as Impulse Antennas, must be very wideband, compatible with impulses and be closely impedance matched over the broad frequency ranges of impulse systems, such as MIR.
Furthermore, there is a growing need for both broadbeam and narrowbeam antennas in the RF/microwave spectrum.
In response to the concerns discussed above, what is needed is a low cost wideband antenna that overcomes the shortcomings of the prior art.
The present invention is a low cost impulse compatible wideband antenna. The antenna may be used for either transmission or reception. Within the system of the present invention, impulse signals travel through a feed point with respect to a ground plane. A geometric fin structure is connected to the feed point, and through a termination resistance to the ground plane. A geometric ridge structure connected to the ground is positioned with respect to the fin in order to receive and radiate electromagnetic energy from the impulse signal at a predetermined impedance and over a predetermined set of frequencies. The fin and ridge can be either a wire or a planar surface.
In another aspect of the invention, the fin and ridge are disposed within a radiation cavity if further direction of the electromagnetic energy is desired. Sidewalls of the cavity may be of various shapes, lengths, and angles with respect to the fin and the ridge.
Within the method of building the present invention, the radiation cavity is constructed of stamped and/or etched metal sheets bent and then soldered together. The fin and ridge are also formed from metal sheets or wires. The fin is attached to the feed point and then to the cavity through a termination resistance. The ridge is attached to the cavity and disposed with respect to the fin in order to achieve a particular set of antenna characteristics.
These and other aspects of the invention will be recognized by those skilled in the art upon review of the detailed description, drawings, and claims set forth below.